Anyone built/listened to D Selfs precision preamp.

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Wondered if anyone had built and or listened to Doug Selfs precision preamp published in August and September 1996 in Electronics World ?

The Signal Transfer Company: Precision Preamplifier

Dougs tone controls with adjustable turnover frequencies look interesting.
The whole design uses NE5532's and does have a fair few electroylitics in the audio path, mainly to keep any offset current out of the pot wiper as it uses NE5532's. Using FET opamps looks a possibilty and would enable these to be ommited.

Anyone any experience of the design in practice :)
 
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Update on this... I prototyped the design and have to say I am very impressed. It's far more useful than "conventional" tone controls due to having continuosly adjustable turnover frequencies and a "return to zero" curve... meaning that it doesn't boost frequencies outside the audio range.

If I ever incorporated the design into a future amp build I would definitely look to using FET opamps and eliminating the electrolytics... but even so... built as published with NE5532's it's excellent.
The only FET opamps I had available (needing 7 of them) were TL072 which often sound better than 5532's particularly as a quick swap in a CD player I/V convertor and filter, but not here... the 5532's are pretty faultless to me :)
 

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Hi Mooly.
Congrats with your D.Self EQ.

Before you get attacked by the "tone-control-is-bad-for-you"-people, I just wanna join your side; Tone Control is good - and often needed!

And especially in these MP3/download times, I think the equaliser really should have a comeback.

As Mark Levinson himself said: "We never said one could do witout tone controls, there just wasn't any that sounded good!" ...wich is double impressive since he practically invented the 'purist' approach wich sported everybody to leave out tonecontrols.

...some music becomes so much more enjoyable with the correct dose of EQ, and that is what it is all about. Try these:
Donald Fagan - the nightfly (add bass - no more 'thin' sounding, but really groovy)
Pink Floyd - Animals (add some in the highest treble - no more muffled sounding, but open and dynamic)


I chose to clone the Audio Palette equalizer instead, and I am as happy as can be.
I am not gonna spoil your happiness, but my Audio Palette clone features:
- Only six controls = intuitive operation
- Well chosen frequencies = attacks the right places
- Range that fits each band = feels 'just right' on all controls.
 
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Thanks for your support :)

I've sat on both sides of the fence when it comes to eq and tone controls... so thought it about time to experiment a little.
I agree with you, some recordings do seem to benefit from a little correction in the right places... and doing it "right" is vitally important.
This tone control stage doesn't wildly accentuate or attenuate in an all or nothing way as most seem to do... it's far far more subtle than that, and makes a real difference truth be told.
I am sure you find yours is similar too.

I would seriously consider adding this to a future complete amp project... it's that good.
 
I built one using the PCB that was (still is?) available. It sounds very good and is very quiet. After 12 years, the input selector switches are starting to stick and crackle, and I don't like the box I used. Will probably re-box it and replace the input selectors with a relay board.

Barry
 
First post, so greetings all. I have been lurking in the background reading and following this good forum:up:.


I built one using the PCB that was (still is?) available. It sounds very good and is very quiet. After 12 years, the input selector switches are starting to stick and crackle, and I don't like the box I used. Will probably re-box it and replace the input selectors with a relay board.

Barry

Hi Barry4,

The original PCB is no longer available - there is a new version with some additions to it such as headphones amp.

The original switch bank parts became a real hassle to source. A custom switch bank is available as a stock-item for the new Precision Preamp. It is NOT compatible with the original PCB.

There may be one or two (literally!) of the original switch banks, or possibly the parts for 1 or 2 switch banks, if you decide to re-switch your Precision Preamp - let me know. Your idea to replace the input selector switches with relays is OK and great for remote control, but please be aware that the switches & their contacts have been laid-out on the PCB in a way that is designed to reduce cross-talk. Note that the circuit schematic shows 2 switch contacts in series - this is to increase physical separation of non-selected active signals from the selected signal. Doing the same thing with relays is recommended.

Hope this helps.

Gareth.
 
Self '96 Pre-amp.

Some may be wondering what the tone control stage actually does in Self's pre-amp. Attached is the measured curves from my build on my own DIY pcb design, 8 yrs ago. Similar to the original in layout, but not in tracking.
It provides the normal boost/cut but with variable turnover frequency.
Snag now is crackly pots. Mooly, where did you get yours. Are they conductive plastic?

Brian.
 

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Hi Garreth... you are too modest :) I believe you were the designer of the original PCB's in question.

Found this on Google showing and detailing the design, starting on page 70 for those that haven't seen the tone control part of the circuit.

Self on Audio - Google Books

Must admit I prefer switching using discrete FET's in a series shunt arrangement... partly for the fact that the performance is consistent over time, and also to use with remote control. And the isolation is better too.
 
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More listening tests in progress... and I wanted to remove those electrolytics too... soooo 10 electroylitics removed and back with the TL072's

Hmmm, in post #2 I commented the 5532's were pretty faultless. Well, must say that so is this set up too. It sounds more "focused" somehow and totally transparent in the center flat position. Can removing those caps really have altered it in that way.

This of course is where subjectivity is flawed in many ways, I know only too well that changes you make "seem" sometimes to be better or worse... often in line with what your expectations may be.
The real test has to be sustained listening, and does it deliver a true musical performance etc. I have to say it does :)

Better opamps would be an obvious thing to try next... I have it on good authority that the LM4562 might be a worthy candidate here. Must look into the DC offset conditions of using that device.
 
Hi Garreth... you are too modest :) I believe you were the designer of the original PCB's in question.

Must admit I prefer switching using discrete FET's in a series shunt arrangement... partly for the fact that the performance is consistent over time, and also to use with remote control. And the isolation is better too.


Hi Mooly,

Yes I was the PCB designer of the original and current boards. Douglas & I have worked together on various projects for many years, and continue to do so. All of the board layouts do, however, get the beady-eye assessment by Douglas before we pass any designs for manufacture.

There are 3 switching topologies that I use - relay, CMOS and FET. All have their plus and minus points and on more complex designs it is not uncommon to use more than one topology - whichever is best for a particular application.

Moving on to op-amps for your EQ: the LM4562 is well worth trying. Its only drawback is its cost!

Cheers,

Gareth.
 
Hello,

I was planning to build a phono stage for my first TT that I'm planning to buy, most probably it will be a Project Debut III.

I was looking for a proofed design, and I also wanted to buy a ready-made PCB.

I found the RIAA Phono and the Precision Preamp. Which made me think of building the Precision Preamp instead somce I don't have one, although this is more expensive.

Is there any advantage in having the Phono stage stand-alone?

What exactly brings the balanced output version?

thanks
 
Hi Mooly,

Yes I was the PCB designer of the original and current boards. Douglas & I have worked together on various projects for many years, and continue to do so. All of the board layouts do, however, get the beady-eye assessment by Douglas before we pass any designs for manufacture.

There are 3 switching topologies that I use - relay, CMOS and FET. All have their plus and minus points and on more complex designs it is not uncommon to use more than one topology - whichever is best for a particular application.

Moving on to op-amps for your EQ: the LM4562 is well worth trying. Its only drawback is its cost!

Cheers,

Gareth.

Curiosity question. Does any audio gear use 4 layer PCBs with a ground plane? I used to design commercial video equipment and the improvement is significant with the ground plane. For audio I've thought of a 4 or even 6 layer board with ground planes on the outer layers and maybe an internal one to totally shield it. Of course you have to get the schematic right as you can't cut traces on the inside layers.

 
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Hi Gareth,
Thank you for dropping in and commenting. Good PCB design from the looks of it. As for the 4562 suggestion, it's a good one. The LME49720 is the other name for this one. For a J-Fet front end, try something along the lines of an OP275 or similar. Cost isn't a large issue with this is it? After all, these do improve the performance and I like the sound quality more, and these determine what your system may sound like. Don't go nuts on op amps, these look like a nice compromise.

Now I have a question for you. BJT and J-Fet op amps are different beasties. Their best low noise range of operation are complimentary, BJT is a low impedance loving device and the J-Fet works better at higher impedance. For example, after a volume control, a J-Fet type should be better. Also, input bias currents for J-Fet types are far lower than most BJT types. No surprises there. Super beta BJT input transistors are in range of J-Fet devices. Were these considerations when deciding which devices to use and in what location?

Hi Mooly,
Most of my preamplifiers do have tone controls, and that doesn't bother me one bit. I'll support you on this. My Cyrus Pre X does not have tone controls. It's also missing a good phono stage (any phono stage!). The only thing I don't like about this product are the signal switching ICs. That's what I think of that commercial design. It sounds good in spite of the built in drawbacks.

Give me switches or relays any day! Nitrogen filled telecom relays are not expensive, and that's the route I would go for a new design. If you don't have a tape deck, or DAT, just short the other inputs out. Marantz had that figured out ages ago.

I'm going to have to search for that preamp article. Doug does understand how to avoid most problems when he designs something.

-Chris
 
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Hmmm... well for some reason I haven't been notified of postings here.

Gareth... yes the LM4562 ;) Cost is an issue of course, yet in the scheme of things it's perhaps worthwhile.

Chris... the original articles go into "why" the 5532 bjt was the prefered choice, and as ever Dougs method is pretty faultless. I'm still kind of "unsure" on the 5532. I think a lot comes down to implementation and most DIY encounters with this device are in DA analogue stages. I read an article recently where it was argued that bjts (like the 5532/4) aren't always the best choice as they can become nonlinear (I guess at a very low level) because of the HF hash from the convertor chip.
Does that sound reasonable "in the real world" or not ?
I have found improvements in subjective quality by swapping 5532's in that particular application (DA) but here as in the preamp, where they are used as totally linear "gain blocks" I have to say they seem excellent.

There is a terrific phono stage in the original articles too... and I have no vinyl lol.
 
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Hi Mooly,
the original articles go into "why" the 5532 bjt was the prefered choice, and as ever Dougs method is pretty faultless.
I still have some reading to do, but I do agree that the 5532 is an excellent performer when properly used (that goes for all op amps). You can't really knock a product using these. Much better than the 1458 or 4558 that are so common these days. I'm not that sure of the TL072 though. It was fabulous when it first popped up in the late 70s. As I recall, the first time I saw it was installed in "Power" DJ mixers nade in France. I was amazed at how quiet it was and just had to dive into one and have a look. I have to believe we have better op amps today for audio use. Of course, you can always use a J-Fet pair, or an LM394 for an input stage with the op amp bringing up the rear. This would be the current state of the art.

-Chris
 
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Hi Chris,
The problem (in theory) with the TL072 in this tone stage is that it can't drive low impedance loads too well. In practice at signal levels I found it worked really well, and I'm hoping to do some much more detailed evaluation on it shortly using some good headphones and this,
http://www.diyaudio.com/forums/head...le-ended-class-headphone-amp.html#post2078604

It's not easy trying to "carry" a particular sound in your head. All I can do is listen for an extended period and try and decide whether the musical presentation is different, better, worse, or just different... and keep coming back and repeating the test. Perhaps with headphones on the bench where it's quicker to swap and change I might come to a more definite conclusion.
Just for fun I always like to pop an 4558 or similar into a circuit, and you can really tell the difference there... it's so obvious yet a bit hard to explain somehow.

My main CD player (MicroMega Stage 2) used two NE5534's, one for for I/V and one for filter buffer in the DAC and replacing these (many years ago) with TLO71's gave a noticeable (and to me worthwhile) change in the sound. I have since swapped these for an OPA604 and AD845... again with really excellent results.
 
Wondered if anyone had built and or listened to Doug Selfs precision preamp published in August and September 1996 in Electronics World ?

The Signal Transfer Company: Precision Preamplifier

Dougs tone controls with adjustable turnover frequencies look interesting.
The whole design uses NE5532's and does have a fair few electroylitics in the audio path, mainly to keep any offset current out of the pot wiper as it uses NE5532's. Using FET opamps looks a possibilty and would enable these to be ommited.

Anyone any experience of the design in practice :)

Does anybody know, what pushbutton switches were used in this Precision Preamplifier?
 
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